> >> Steve, What do you think of this idea.
> >>
> >> Since we will not be flying forward in helicopter mode for long > or at
> >> high speed
> >> the leading and lagging hinges can be done away with. Same goes > for the
> >> flapping
> >> hinges. I think we can use GRP for the hub. Same as several > European>> helicopters
> >> use. GRP has high tensile strength and a low modulus of elasticity> >> allowing it to
> >> flex without failing. Same as the Long EZ main landing gear. The
> >> innovative feature
> >> of having a one piece carbon fiber blade with internal outer > bearing race
> >> and pitch
> >> change arm is also a major weight and cost saving feature. The > bearing>> balls are
> >> Torlon which are widely used in off shore sail boat racing. > These are
> >> subject
> >> to the worst possible environmental conditions and survive. The
> >> connection
> >> between blade and hub is achieved by the bearing balls and they > are fed
> >> into the races by one access hole on each side. We have used this
> >> feature in the past of an aircraft propeller and it works well.
> >> -- > >> Paul Lamar ...No rotor no motor.
> >
> >
> > Go one step further and use a standard prop internal pitch change
> > mechanism.
> > Milo
> >
> > Care to make a 3D dwg for me? I can't see how it would work with > counter> rotating
> > rotors?
> >
> > Paul Lamar
> > Forgot about that! Milo
> > That is why I went with the tried and true helicopter pitch change.
> > -- > Paul Lamar ...No rotor no motor.
> > > > I think it would start shaking pretty good as soon as you started > gettingsome translational lift.  Did you look at that website I sent?> http://www.rotor-international.net/
> > It uses co-axial two-blade rotors and they appear to be underslung > withshort beams that twist for feathering, flex for coning and may > be servo-tab
> controlled.  Look at how far apart the rotors are.  I think if you > want the
> flexure to to accomplish lead and lag, the flexible portion should be
> outside the feathering bearings.  The stiffer the system is, the > more moment
> applied to the hub and the more vibration.
> > I think on the model you've shown, with one bearing race, when a > moment is
> applied to the assembly the loads on the bearings could get pretty > high.  A
> second bearing race inboard would help, especially if it were an > angularcontact type that could take high thrust loads and it was > located far enough
> inboard to resist to the applied moment.  I'm not sure about those > Torlonbearings being strong enough, but with two races, they might > be and you
> would avoid the shear load that would occur with your model and > the loads
> would be all compressive.  The slight elasticity of the Torlon may > helpdistribute the load which would be a good thing as well.
> > Steve
> > I don't think so. We don't do much translational lift. It is an > arcing takeoff with
> considerable vertical velocity for only a second or two.
> > I looked at that web site but  I saw no details of the hubs. If > you see something
> there in detail please do a screen capture and email that.
> > All constant speed props are built with only one bearing. The > negative bending
> moment on the blade hinge due to centripetal force acting on the > blade CG counteracts
> the positive bending moment due to thrust. Therefore it only needs > one bearing.
> > If the constant cord blade weighs 20 pounds
> and it moves up one foot at it's CG radius position that is a > negative bending moment
> of 100,000 foot pounds. The centripetal force on the 20 pound > blade is 100,000 pounds.
> Weight/32.2 x FPS^2.  The positive bending moment due to thrust on > the blade is only
> 6.5 ft x 300 pounds (each of four blades will need to generate 300 > pounds to lift the
> 1200 pound craft.) or about 2000 foot pounds.
> > Obviously the rotor blade CG is not going to move up one foot. The > upwardsdeflection of the blade at its CG position will only be > about .2 feet or 2.4 inches
> balancing the thrust moment. That puts a negligible bending load > on the bearing compared
> to the centripetal load. All props and rotors work this way. If > not rotors and blades
> would break  off at the hub because they do not have the bending > strength on their own
> to support the weight of the helicopter.
> > The bearing consists of 22 half inch dia. balls. In effect they > act like 22 1/2 inch
> dia. bolts in single shear. The centripetal load is 100,000 pounds > so each half inch
> bolt only needs to accept 4,500 pounds of shear roughly. A 1/2 > inch bolt has an area
> of about .2 square inches. So the shear stress on the bolt will be > 22,500 psi
> roughly. A piece of cake for a steel ball but maybe marginal for a > Torlonball. Consequently I will try to get the carbon fiber blade > weight well below
> 20 pounds each.
> > As you can see the centripetal force is orders of magnitude higher > than the
> bending loads on the blade hub. It is all about numbers.
> > Paul Lamar ...No rotor no motor.

I don't think I can add too much to the discussion as heli dynamic's are
something I've never studied to extensively [primarily because I
never come across any books on it] but I do think there will be
times when there is signifigant translational lift. I'm thinking of
landing more than take-off. When the pilot pulls up and starts to
drop forward speed and translate into vertical flight. This isn't
a problem on your average aerobatic a/c however, so maybe
it won't be such an issue as long as there isn't abrupt control
movements exceeding some G number?

Not entirely sure..

Jarrett

A lot of prop helio hubs have lead lag dampers so they could be added.

Perhaps. I can send a dwg and you could do an FEA. I am curios about the
bending deflection of the FRP and the loads on the bearing balls.
I changed the design and did away with the inner bearing.

What would help is a simple FEA of one 1/2 inch ball and sections of the races.
I'll do a 3D of just that.

Paul Lamar ...No rotor no motor.

Send away.. I'll throw it in and see what it shows..

Jarrett

Put in 10,000 pounds of shear and see what happens. High strength steel.
and then aluminum to simulate the Torlon.

Unless of course you can put in the Torlon properties directly.

Just think what would happen if we showed up at Reno with a delta tilt rotor
and said: "We want to race."  Their response would be price less :)